Development of transgenic collards (Brassica oleracea L., var. acephala) expressing a cry1Ac or cry1C Bt gene for control of the diamondback moth

Collards (Brassica oleracea var. acephala) are an important vegetable crucifer produced worldwide for human consumption, and one subject to severe injury by Lepidoptera. We have produced Bacillus thuringiensis (Bt)-transgenic collard lines that have the potential to be used either for direct control or as a “dead end” trap crop for Lepidoptera. To produce collard lines expressing Bt genes, a cry1Ac Bt gene, in association with the nptII gene for kanamycin-resistance, and a cry1C Bt gene, in association with the hpt gene for hygromycin-resistance, were introduced into seedling explants by Agrobacterium tumefaciens-mediated transformation. A total of 30 kanamycin-resistant and 28 hygromycin-resistant plants were regenerated from two collard cultivars (“McCormack's Green Glaze” [glossy leaves] and “Champion” [non-glossy leaves]). PCR assays of the kanamycin- and hygromycin-resistant plants and Southern analyses of the hygromycin-resistant Champion plants confirmed the presence and integration of the associated Bt genes. ELISA analyses of leaf tissue from the antibiotic-resistant plants showed that production of the Cry1Ac and Cry1C Bt proteins varied greatly among independent transformants, ranging from undetectable to over 2000 ng of Bt protein/mg of total soluble protein. All cry1Ac and cry1C collard plants in which Bt protein was detected caused complete mortality of larvae from susceptible diamondback moth, Plutella xylostella. Cry1Ac-transgenic plants also controlled P. xylostella populations resistant to Cry1C protein, while cry1C-transgenic plants controlled Cry1Ac-resistant P. xylostella. Sexual crosses have produced lines with both Bt genes. “McCormack's Green Glaze” plants were more attractive for P. xylostella oviposition than cabbage plants and hence are suitable for use as “dead end” trap crops. If approved for human consumption in the future, Bt collards could serve not only as a trap crop but also as a cash crop, thereby expanding the traditional role of a trap crop. This example of Bt collards illustrates the potential for using biotechnology in multiple ways for insect control.